Pakistan's coalition Government leader Asif Ali Zardari is looking for new supporters after a split with rival politician Nawaz Sharif.

Former prime minister Mr Sharif announced that he was withdrawing from the Government at a press conference in Islamabad.

He said he was pulling out because of Mr Zardari's failure to honour promises to reinstate judges sacked by former president Pervez Musharraf, and to select a non-partisan candidate to replace Mr Musharraf.

He has also nominated a former chief justice to run against Mr Zardari in the presidential election on September 6.

Mr Zardari is the widower of assassinated former prime minister Benazir Bhutto.

"We therefore feel that these repeated defaults and violations have forced us to withdraw our support from the ruling coalition and sit on the opposition benches," Mr Sharif told the news conference.

The departure of his party is not expected to force a general election as Mr Zardari's Pakistan People's Party (PPP) should be able to gather enough support to govern, analysts say.

The coalition, formed after Mr Musharraf's allies lost a February parliamentary election, had looked increasingly precarious since Mr Musharraf resigned a week ago.

Mr Sharif's party repeatedly threatened to leave the coalition if judges Mr Musharraf purged last year were not restored to office. Last week, he set Monday as his latest deadline.